Specfix: switch to Psych for YAML test

On Ruby 2.6 and 2.7 the bundled version of YAML has an inconsistent
interface (YAML.unsafe_load, YAML.safe_load and YAML.load) are not
consistently present. So embrace the gem version of the underlying
library (Psych) and simply use the latest version.

Gemfile

@@ -5,6 +5,7 @@ source 'https://rubygems.org'
 # Specify your gem's dependencies in groupie.gemspec
 gemspec
 
+gem 'psych', '~> 4.0'
 gem 'rake', '~> 13.0'
 gem 'rspec', '~> 3.0'
 gem 'rubocop', '~> 1.7'

Gemfile.lock

@@ -11,6 +11,8 @@ GEM
     parallel (1.21.0)
     parser (3.1.0.0)
       ast (~> 2.4.1)
+    psych (4.0.3)
+      stringio
     rainbow (3.1.1)
     rake (13.0.6)
     regexp_parser (2.2.1)
@@ -47,6 +49,7 @@ GEM
     rubocop-rspec (2.8.0)
       rubocop (~> 1.19)
     ruby-progressbar (1.11.0)
+    stringio (3.0.1)
     unicode-display_width (2.1.0)
 
 PLATFORMS
@@ -56,6 +59,7 @@ PLATFORMS
 
 DEPENDENCIES
   groupie!
+  psych (~> 4.0)
   rake (~> 13.0)
   rspec (~> 3.0)
   rubocop (~> 1.7)

spec/groupie_spec.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 require 'spec_helper'
-require 'yaml'
+require 'psych'
 
 RSpec.describe Groupie do
   it 'has a version' do
@@ -286,7 +286,9 @@
     groupie['one'].add %w[buy flowers]
     groupie['two'].add %w[buy roses]
 
-    loaded = YAML.unsafe_load(YAML.dump(groupie))
+    # Use Psych via a Gem to have a consistent library interface vs older versions in older Ruby versions
+    yaml = Psych.dump(groupie)
+    loaded = Psych.safe_load(yaml, aliases: true, permitted_classes: [Groupie, Groupie::Group, Set])
 
     expect(loaded.classify_text(%w[buy candy])).to eq(groupie.classify_text(%w[buy candy]))
   end